The polyphenylene ether resins are a family of engineering thermoplastics known to be admixable with other polymeric materials, such as styrenic copolymeric impact modifiers, to form blends which can be molded into articles of various shapes and sizes. The polyphenylene ether resins and methods of their preparation are described in U.S. Pat. Nos. 3,306,874 and 3,306,875 (Hay), in U.S. Pat. Nos. 3,257,357 and 3,257,358 (Stamatoff), and elsewhere. Styrenic polymers suitable for admixture with the polyphenylene ether resins are described in U.S. Pat. No. 3,383,435 (Cizek), and elsewhere.
In general, mineral fillers, such as clay, titanium dioxide, silica, and the like, when incorporated into thermoplastic blends provide greater rigidity and stiffness in the molded or shaped article, as manifested by increases in the modulus, dimensional stability and heat distortion temperature. The use of various mineral fillers in polyphenylene ether resin compositions is described in the patent literature. For instance, mixtures of polyphenylene ether resin, rubber modified high impact polystyrene and aluminum silicate are disclosed in U.S. Pat. No. 4,166,812 (Lee, Jr.). The utility of small particle clay and of small particle titanium dioxide (in both cases, no greater than 0.6 micron in diameter) in plasticized compositions of a polyphenylene ether resin and an ABA block copolymer is disclosed by Abolins, in U.S. Pat. Nos. 4,317,761 and 4,318,836, respectively.
While the presence of mineral fillers confers the aforementioned benefits, in the typical case other important physical properties such as the impact strength, tensile elongation (ductility), optical properties and processability are adversely affected. These adverse effects are attributable to the fact that the polymer and mineral filler have poor compatibility and do not adhere well to one another. A result is that the amount of mineral filler which can be used is very limited if large increases in the melt viscosity are to be avoided, and even with smaller filler amounts the compositions must usually be processed at higher temperatures to compensate for the poorer melt flow.